Fail if variable does not match a regular expression

Question

Looking for an Ansible task that will fail the playbook if a variable does not match a given regex. Something like:

# fail when hostname doesn't match a regex
- fail:
    msg: "The inventory hostname must match regex"
  when: {{ inventory_hostname }} not matches [a-z](([-0-9a-z]+)?[0-9a-z])?(\.[a-z0-9](([-0-9a-z]+)?[0-9a-z])?)*

Answer 1

You probably want to use the assert module:

- assert:
    that:
    - inventory_hostname | match('your regex')

See also Playbook Tests and Filters